462 ZOOLOGY — 
smaller claws, shaped like those of the Spermophiles. The hind soles are 
entirely naked, without any conspicuous tubercles; the heel is naked and 
narrow. 
“These little sand rats,” says Dr. Richardson, ‘‘are numerous in the 
neighborhood of Fort Vancouver, where they inhabit the declivities of low 
hills, and burrow in the sandy soil. They feed on acorns, nuts (Corylus 
rostrata), and grass, and commit great havoc in the potato fields adjoining 
the fort, not only by eating the potatoes on the spot, but by carrying off 
large quantities of them in their pouches.” | 
The genus Saccomys is founded upon a North American Geomys. 
The genus Perognathus was created for a new species inhabiting the 
upper Missouri. The genus Heteromys contains two species; one inhabits 
Central America, the other Colombia and Guiana. The genera Macroco- 
lus and Dipodomys are Mexican, and include each only one species. 
Dipodomys phillipsu is the well known jumping or kangaroo rat of 
California. 
Sub-jum. 2. Bathyergina, composed only of the genera Bathyergus and 
Georychus, the first with one, the second with two species, all three from 
southern Africa. The Bathyergus capensis burrows in the sand flats of 
the Cape of Good Hope in very great numbers. In every part of these flats 
mole-hills are observed, and when walking on the surface the foot often 
sinks into their galleries, thus making it very dangerous to ride on horse- 
back in those localities, owing to the danger of being thrown by the unex- 
pected sinking of the horse’s feet into these holes. 
Sub-fam. 8. Arvicolina, have, like the rats (Murina), three molars above 
and below on each side, but rootless, each one being composed of triangular 
prisms, placed on two alternate lines. 
The genus Arvicola includes the common field-rats, which have a hairy 
cylindrical tail, shorter than the body, and the ears clothed with hair. The 
fore feet have four toes and a rudimentary thumb; the hind feet are five- 
toed, furnished with weak nails. They burrow in the earth and feed on 
grain, bulbous roots, and grasses; some are omnivorous, they do not climb, 
are not dormant in winter, but seek their food during cold weather, eating 
roots, grasses, and the bark of trees. 
The species of this genus are found all over the world; nine of them 
belong to North America. The meadow mouse or campagnol (A. pennsyl- 
vanica) is very abundant in the northern and eastern United States, and 
extends northwards as far as Hudson’s Bay, and westwards to the banks 
of the Ohio. It swims and dives well. A dozen more species are found in 
North America; some inhabit the Eastern States, others belong to the 
western territories, Texas, Oregon, California, &c. 
The genus Lemmus (the lemmings) includes those Arvicolina which 
have very short ears and tails, and the toes of the fore feet adapted for 
digging. There are five distinct nails to the fore feet. The species of 
this genus are peculiar to the northern hemisphere. One of them, of the 
size of a large rat, is celebrated for its occasional migrations in innumerable 
bodies. At these periods they are said to march in a straight line, regard- 
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